Facilitated CO2 transport membrane, method for producing same, resin composition for use in method for producing same, CO2 separation module and method and apparatus for separating CO2

ABSTRACT

Provided is a facilitated CO 2  transport membrane having improved CO 2  permeance and improved CO 2  selective permeability. The facilitated CO 2  transport membrane includes a separation-functional membrane comprising a hydrophilic polymer gel membrane which contains a CO 2  carrier and a CO 2  hydration catalyst, wherein the hydrophilic polymer is a copolymer including a first structural unit derived from an acrylic acid cesium salt or an acrylic acid rubidium salt and a second structural unit derived from vinyl alcohol. More preferably, the CO 2  hydration catalyst has catalytic activity at a temperature of 100° C. or higher.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase filing under 35 U.S.C. §371 ofInternational Application No. PCT/JP2014/058047 filed on Mar. 24, 2014,which claims priority to Japanese Patent Application No. 2013-073644filed on Mar. 29, 2013.

PARTIES TO A JOINT RESEARCH AGREEMENT

Renaissance Energy Research Corporation, a corporation of Japan, andSumitomo Chemical Company, Limited, a corporation of Japan, are partiesto a Joint Research Agreement.

TECHNICAL FIELD

The present invention relates to a facilitated CO₂ transport membranefor use in separating carbon dioxide (CO₂), particularly to afacilitated CO₂ transport membrane designed to separate carbon dioxidewith high CO₂ selective permeability from a mixed gas containing carbondioxide and at least one gas selected from hydrogen, helium, nitrogen,oxygen, carbon monoxide, hydrocarbon (such as methane, ethane, orpropane), and unsaturated hydrocarbon (such as ethylene or propylene)and the like. The present invention further relates to a method forproducing the facilitated CO₂ transport membrane and to a method and anapparatus for separating CO₂ using the facilitated CO₂ transportmembrane.

BACKGROUND ART

A chemical absorption method is used in a decarbonation processperformed in existing large-scale plants for hydrogen production, ureaproduction, or the like. To separate CO₂, such a chemical absorptionmethod requires a huge CO₂ absorption tower and a huge tower forregenerating a CO₂ absorbing liquid. The step of regenerating the CO₂absorbing liquid also wastefully consumes energy because it requires alarge amount of steam to remove CO₂ from the CO₂ absorbing liquid byheating for the reuse of the liquid.

In recent years, as a countermeasure for global warming, natural energythat does not emit CO₂ has been expected to come into wide use, butnatural energy has a significant problem in terms of cost. Thus,attention has been paid to a method called CCS (Carbon dioxide Captureand Storage) in which CO₂ is separated and collected from waste gasesfrom thermal power plants, ironworks and the like, and buried in theground or sea. Currently, even CCS is based on application of thechemical absorption method. In this case, for separating and collectingCO₂ from thermal power plants, not only large-scale CO₂ separationequipment is required, but also a large amount of steam should be fed.

Besides separation and collection of CO₂ from waste gases from thermalpower plants and the like, for example, purification of natural gas as amajor energy source requires separation of CO₂ because it containsseveral % of CO₂ in addition to methane as a main component. A chemicalabsorption method is used in existing processes for such purification.

On the other hand, a CO₂ separation and collection process using amembrane separation method is intended to separate a gas by means of adifference in velocity of gases passing through a membrane using apartial pressure difference as driving energy, and is expected as anenergy-saving process because the pressure of a gas to be separated canbe utilized as energy and no phase change is involved.

Gas separation membranes are broadly classified into organic membranesand inorganic membranes in terms of a difference in membrane material.The organic membrane has the advantage of being inexpensive andexcellent in moldability as compared to the inorganic membrane. Theorganic membrane that is used for gas separation is generally a polymermembrane prepared by a phase inversion method, and the mechanism ofseparation is based on a solution-diffusion mechanism in which a gas isseparated by means of a difference in solubility of the gas in themembrane material and diffusion rate of the gas in the membrane.

The solution-diffusion mechanism is based on the concept that a gas isfirst dissolved in the membrane surface of a polymer membrane, and thedissolved molecules diffuse between polymer chains in the polymermembrane. Where for a gas component A, the permeability coefficient isP_(A), the solubility coefficient is S_(A), and the diffusioncoefficient is D_(A), the relational expression: P_(A)=S_(A)×D_(A)holds. The ideal separation factor α_(A/B) is expressed asα_(A/B)=P_(A)/P_(B) by taking the ratio of permeability coefficientsbetween components A and B, and thereforeα_(A/B)=(S_(A)/S_(B))×(D_(A)/D_(B)) holds. Here, S_(A)/S_(B) is referredto as solubility selectivity, and D_(A)/D_(B) is referred to asdiffusivity selectivity.

Since the diffusion coefficient increases as the molecular diameterdecreases, and the contribution of diffusivity selectivity is generallygreater than that of solubility selectivity in gas separation, it isdifficult to allow selective passage of gases having a larger moleculardiameter by suppressing passage of gases having a smaller moleculardiameter among multi-component gases having different moleculardiameters.

Thus, studies are conducted on a permeable membrane called a facilitatedtransport membrane that allows selective permeation of a gas by afacilitated transport mechanism, in addition to a solution-diffusionmechanism, using a substance called a “carrier” which selectively andreversibly reacts with CO₂ (see, for example, Patent Document 1 below).The facilitated transport mechanism has a structure in which a membranecontains a carrier which selectively reacts with CO₂. In the facilitatedtransport membrane, CO₂ passes not only physically by thesolution-diffusion mechanism but also as a reaction product with thecarrier, so that the permeation rate is accelerated. On the other hand,gases such as N₂, CH₄ and H₂, which do not react with the carrier, passonly by the solution-diffusion mechanism, and therefore the separationfactor of CO₂ with respect to these gases is extremely high. Energygenerated during the reaction of CO₂ with the carrier is utilized asenergy for releasing CO₂ by the carrier, and therefore there is no needto supply energy from outside, so that an essentially energy-savingprocess is provided.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: International Publication No. WO 2009/093666

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Patent Document 1 proposes a facilitated CO₂ transport membrane having aCO₂ permeance and a CO₂/H₂ selectivity feasible at a high temperaturecondition of 100° C. or higher by using as a carrier a specific alkalimetal salt such as cesium carbonate or rubidium carbonate.

The facilitated CO₂ transport membrane has a higher CO₂ permeation rateas compared to a membrane based on a solution-diffusion mechanism, butthe number of carrier molecules that react with CO₂ molecules becomesless sufficient as the partial pressure of CO₂ increases, and thereforeimprovement is required for accommodating the membrane to carriersaturation even at such a high CO₂ partial pressure.

In view of the above-mentioned problems, it is an object of the presentinvention to stably supply a facilitated CO₂ transport membrane havingan improved CO₂ permeance and an improved CO₂ selective permeability.

Means for Solving the Problems

To achieve the object, the present invention provides a facilitated CO₂transport membrane comprising a separation-functional membrane whichcomprises a hydrophilic polymer gel membrane that contains a CO₂ carrierand a CO₂ hydration catalyst, wherein the hydrophilic polymer is acopolymer comprising a first structural unit derived from an acrylicacid cesium salt or an acrylic acid rubidium salt and a secondstructural unit derived from vinyl alcohol. It is to be noted that theCO₂ hydration catalyst is a catalyst capable of increasing the rate ofthe CO₂ hydration reaction shown in the following (Chemical Formula 1).The symbol “

” in the reaction formulae shown herein indicates that the reaction isreversible.CO₂+H₂O

HCO₃ ⁻+H⁺  (Chemical Formula 1)

The reaction of CO₂ with the CO₂ carrier is expressed by the following(Chemical Formula 2) as an overall reaction formula. It is to be notedthat the (Chemical Formula 2) is based on the assumption that the CO₂carrier is a carbonate. The CO₂ hydration reaction, one of elementaryreactions of the above-mentioned reaction, is an extremely slow reactionunder a catalyst-free condition, and addition of a catalyst acceleratesthe elementary reaction, so that the reaction of CO₂ with the CO₂carrier is accelerated, and as a result, improvement of the permeationrate of CO₂ is expected.CO₂+H₂O+CO₃ ²⁻

2HCO₃ ⁻  (Chemical Formula 2)

Thus, since the facilitated CO₂ transport membrane having theabove-mentioned features contains a CO₂ carrier and a CO₂ hydrationcatalyst in a separation-functional membrane, the reaction of CO₂ withthe CO₂ carrier is accelerated, so that a facilitated CO₂ transportmembrane having an improved CO₂ permeance and an improved CO₂ selectivepermeability can be provided. Further, since the CO₂ hydration catalysteffectively functions even at a high CO₂ partial pressure, the CO₂permeance and CO₂ selective permeability at a high CO₂ partial pressureare each improved. Further, since the separation-functional membrane iscomposed of a gel membrane rather than a liquid membrane or the like,high CO₂ selective permeability can be stably exhibited even underpressure.

As a result of extensive studies, the inventors of the presentapplication have further found that when a copolymer including a firststructural unit derived from an acrylic acid cesium salt or an acrylicacid rubidium salt and a second structural unit derived from vinylalcohol is used as a hydrophilic polymer to form a gel membrane, thecopolymer can provide further improved CO₂ permeance as compared with ageneral polyvinyl alcohol-polyacrylic acid salt copolymer (PVA/PAAsodium salt copolymer), which has a sodium salt as an acrylic acid saltand the use of which is shown in Patent Document 1, so that CO₂permeance and CO₂ selective permeability under high CO₂ partial pressurecan be further improved, respectively.

In the facilitated CO₂ transport membrane with the above features, thegel membrane is a hydrogel in which a three-dimensional networkstructure is formed when the hydrophilic polymer is crosslinked andwhich has the property of being swollen when absorbing water. Therefore,the gel membrane, which is composed of a hydrogel having a highwater-holding capacity, can hold water as much as possible even at ahigh temperature capable of causing a reduction in the water content ofthe separation-functional membrane, so that high CO₂ selectivepermeability can be achieved.

Further, in the facilitated CO₂ transport membrane having theabove-mentioned features, the CO₂ hydration catalyst preferably hascatalytic activity at a temperature of 100° C. or higher. The reactionof CO₂ with the CO₂ carrier is thereby accelerated at a temperature of100° C. or higher, so that a facilitated CO₂ transport membrane havingan improved CO₂ permeance and an improved CO₂ selective permeability canbe provided under such a temperature condition.

Further, in the facilitated CO₂ transport membrane having theabove-mentioned features, the CO₂ hydration catalyst preferably has amelting point of 200° C. or higher, and is preferably soluble in water.

In the facilitated CO₂ transport membrane with the above features, theCO₂ hydration catalyst preferably comprises an oxo acid compound, and inparticular, the CO₂ hydration catalyst preferably comprises an oxo acidcompound of at least one element selected from group 14 elements, group15 elements, and group 16 elements. More preferably, the CO₂ hydrationcatalyst comprises at least one of a tellurous acid compound, aselenious acid compound, an arsenious acid compound, and an orthosilicicacid compound.

Particularly, when the melting point of the CO₂ hydration catalyst is200° C. or higher, the catalyst can exist in the separation-functionalmembrane while being thermally stable, so that performance of thefacilitated CO₂ transport membrane can be maintained over a long periodof time. Further, when the CO₂ hydration catalyst is soluble in water, ahydrophilic polymer gel membrane containing a CO₂ hydration catalyst canbe easily and stably prepared. When a tellurous acid compound, anarsenious acid compound or a selenious acid compound is used as the CO₂hydration catalyst, stable improvement of membrane performance can beexpected because all of these compounds are water soluble and have amelting point of 200° C. or higher.

In the facilitated CO₂ transport membrane with the above features, acontent of the second structural unit in the hydrophilic polymer ispreferably from 1 mol % to 90 mol % with respect to the total content ofthe first and second structural units.

In the facilitated CO₂ transport membrane with the above features, theCO₂ carrier preferably comprises at least one of an alkali metalcarbonate, an alkali metal bicarbonate, and an alkali metal hydroxide,and the alkali metal is preferably cesium or rubidium. These featurescan further ensure high CO₂ selective permeability.

Here, a reaction expressed by the above (Chemical Formula 2) occurs whenthe CO₂ carrier is a carbonate of an alkali metal, while a reactionexpressed by the following (Chemical Formula 3) occurs when the CO₂carrier is a hydroxide of an alkali metal. The (Chemical Formula 3)shows a case where the alkali metal is cesium as an example.CO₂+CsOH→CsHCO₃CsHCO₃+CsOH→Cs₂CO₃+H₂O  (Chemical Formula 3)

The reactions in the above (Chemical Formula 3) can be united into areaction expressed by the (Chemical Formula 4). That is, this shows thatadded cesium hydroxide is converted into cesium carbonate. Further, itis apparent from the above (Chemical Formula 3) that a similar effectcan be obtained when as a CO₂ carrier, a bicarbonate is added in placeof a carbonate of an alkali metal.CO₂+2CsOH→Cs₂CO₃+H₂O  (Chemical Formula 4)

Further, in the facilitated CO₂ transport membrane having theabove-mentioned features, the separation-functional membrane ispreferably supported by a hydrophilic porous membrane.

First, when the separation-functional membrane is supported by theporous membrane, the strength of the facilitated CO₂ transport membraneat the time of use is improved. As a result, a sufficient membranestrength can be secured even when a pressure difference between bothsides of the facilitated CO₂ transport membrane (inside and outside of areactor) is large (e.g. 2 atm or larger).

In addition, when the separation-functional membrane as a gel membraneis supported by a hydrophilic porous membrane, the gel membrane can bestably formed with less defects. The hydrophilic porous membrane isintended to also include a membrane produced by hydrophilization of ahydrophobic porous membrane.

A coating liquid can be provided as a resin composition that comprises amedium containing water, the copolymer as a hydrophilic polymercomprising the first and second structural units, a CO₂ carrier, and aCO₂ hydration catalyst. When the coating liquid is applied to thehydrophilic porous membrane, the pores of the porous membrane is filledwith the coating liquid, and the coating liquid is further deposited onthe surface of the porous membrane. When the medium is removed from theresultant coating, a separation-functional membrane can be produced inthe form of a gel. In this case, the gel membrane can be deposited notonly on the surface of the porous membrane but also in the pores of theporous membrane, so that defects are less likely to occur and the gelmembrane can be produced at a high success rate. The medium may alsocomprise a water-soluble organic solvent in addition to water. Theamount of the medium is preferably such that the resultant coatingliquid can be kept homogeneous. The medium may be removed from thecoating by any method. The medium may be removed by heating, pressurereduction, or natural drying. Preferably, the medium is removed in sucha manner that it can partially remain in the coating.

The porous membrane provided to support the separation-functionalmembrane does not always have to be hydrophilic although it ispreferably hydrophilic as mentioned above. A non-defective gel membranecan be formed even on a hydrophobic porous membrane, for example, byincreasing the thickness of the coating.

Further, the separation-functional membrane supported by the hydrophilicporous membrane is preferably covered with a hydrophobic porousmembrane. The separation-functional membrane is thereby protected by thehydrophobic porous membrane, leading to a further increase in strengthof the facilitated CO₂ transport membrane at the time of use. Theseparation-functional membrane is covered with the hydrophobic porousmembrane, and therefore even when steam is condensed on the membranesurface of the hydrophobic porous membrane, water is repelled andthereby prevented from penetrating the separation-functional membranebecause the porous membrane is hydrophobic. Accordingly, the hydrophobicporous membrane can prevent a situation in which the CO₂ carrier in theseparation-functional membrane is diluted with water, and the dilutedCO₂ carrier flows out of the separation-functional membrane.

The present invention further provides a method for producing thefacilitated CO₂ transport membrane with the above features. The methodcomprises the steps of applying to a porous membrane a coating liquidcomprising a medium containing water, the hydrophilic polymer, the CO₂carrier, and the CO₂ hydration catalyst; and removing the medium fromthe resultant coating to produce the separation-functional membrane inthe form of a gel.

According to the facilitated CO₂ transport membrane-producing methodwith the above features, the coating liquid can be previously preparedso as to have a suitably adjusted ratio of the CO₂ carrier and thewater-soluble CO₂ hydration catalyst to the hydrophilic polymer, so thatthe mixing ratio of the CO₂ carrier and the CO₂ hydration catalyst inthe final gel membrane can be easily made suitable, which makes itpossible to provide a high-performance membrane.

The present invention further provides a CO₂ separating methodcomprising the steps of: supplying a CO₂-containing mixed gas to thefacilitated CO₂ transport membrane with the above features; andseparating from the mixed gas the CO₂ having permeated the facilitatedCO₂ transport membrane.

The present invention further provides a CO₂ separation membrane modulecomprising the facilitated CO₂ transport membrane with the abovefeatures.

The present invention further provides a CO₂ separation apparatuscomprising: the facilitated CO₂ transport membrane with the abovefeatures; a gas supply unit configured to supply a CO₂-containing mixedgas to the facilitated CO₂ transport membrane; and a gas separation unitconfigured to separate from the mixed gas the CO₂ having permeated thefacilitated CO₂ transport membrane.

The present invention further provides a resin composition for use inthe production of the facilitated CO₂ transport membrane with the abovefeatures. The resin composition comprises a CO₂ carrier, a CO₂ hydrationcatalyst, and a copolymer comprising a first structural unit derivedfrom an acrylic acid cesium salt or an acrylic acid rubidium salt and asecond structural unit derived from vinyl alcohol.

Effects of the Invention

According to the features of the facilitated CO₂ transport membrane andthe method for the production thereof, facilitated CO₂ transportmembranes with an improved level of CO₂ permeance and CO₂ selectivepermeability can be provided stably.

In addition, according to the features of the method and apparatus forseparating CO₂, CO₂ can be selectively separated with high efficiencyfrom a CO₂-containing mixed gas by using the facilitated CO₂ transportmembrane having high CO₂ selective permeability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing a structure in oneembodiment of a facilitated CO₂ transport membrane according to thepresent invention.

FIG. 2 is a flow chart showing an example of a method for producing afacilitated CO₂ transport membrane according to the present invention.

FIG. 3 is a table showing a list of constitutional conditions andmembrane performance for separation-functional membranes of Examples 1to 7 and Comparative Examples 1 and 2 used in experiments for evaluationof membrane performance of a facilitated CO₂ transport membraneaccording to the present invention.

FIG. 4 is a graph showing a CO₂ permeance and a CO₂/H₂ selectivity inExamples 1 to 3 and 7 and Comparative Examples 1 and 2 shown in FIG. 3.

FIG. 5 is a graph showing a CO₂ permeance and a CO₂/H₂ selectivity inExamples 4 to 6 shown in FIG. 3.

FIG. 6 is a graph showing a CO₂ permeance and a H₂ permeance in Examples1 to 7 shown in FIG. 3.

FIG. 7 is a table showing a list of constitutional conditions andmembrane performance for separation-functional membranes of Examples 8and 9 and Comparative Example 3 used in experiments for evaluation ofmembrane performance of a facilitated CO₂ transport membrane accordingto the present invention.

FIGS. 8A and 8B are configuration diagrams each schematically showing anoutlined configuration in one embodiment of a CO₂ separation apparatusaccording to the present invention.

DESCRIPTION OF EMBODIMENTS

By extensively conducting studies, the inventors of the presentapplication have found that when a gel membrane of a facilitated CO₂transport membrane, which contains a CO₂ carrier and in which a reactionof CO₂ with the CO₂ carrier as expressed by the above (Chemical Formula2) occurs, contains a catalyst for a CO₂ hydration reaction as expressedby the above (Chemical Formula 1), one of elementary reactions of theabove-mentioned reaction, the catalyst being capable of maintainingcatalytic activity without being deactivated at a high temperature of100° C. or higher, the CO₂ permeance is dramatically improved withrespect to the H₂ permeance even at such a high temperature, and the CO₂selective permeability is considerably improved as compared to aconventional facilitated CO₂ transport membrane that does not containthe catalyst (first new finding).

The inventors of the present application have further found that whenformed using a gel membrane composed of a copolymer including a firststructural unit derived from an acrylic acid cesium salt or an acrylicacid rubidium salt and a second structural unit derived from vinylalcohol, the facilitated CO₂ transport membrane can have furtherimproved CO₂ permeance and further improved CO₂ selective permeabilityas compared with conventional facilitated CO₂ transport membranes formedusing a PVA/PAA sodium salt copolymer (second new finding).

The inventors of the present invention also have found that the two newfindings are synergistically effective without interfering with eachother so that the CO₂ permeance and the CO₂ selective permeability canbe made higher than those obtained when each technique is preformedalone. Finally, based on the two new findings, the inventors of thepresent application have invented a facilitated CO₂ transport membrane,a method for the production thereof, a resin composition for use in theproduction method, a CO₂ separation module, and a method and anapparatus for separating CO₂, which will be described below.

First Embodiment

First, an embodiment of a facilitated CO₂ transport membrane, anembodiment of a method for the production thereof, and an embodiment ofa resin composition for use in the production method, according to thepresent invention (hereinafter, referred to as “the present facilitatedtransport membrane,” “the present production method,” and “the presentresin composition,” respectively, as needed) will be described withreference to the drawings.

The present facilitated transport membrane is a facilitated CO₂transport membrane including a separation-functional membrane thatincludes a water-containing hydrophilic polymer gel membrane containinga CO₂ carrier and a CO₂ hydration catalyst having catalytic activity ata temperature of 100° C. or higher, the facilitated CO₂ transportmembrane having a high CO₂ permeance and a high CO₂ selectivepermeability. To stably exhibit a high CO₂ selective permeability, thepresent facilitated transport membrane further includes a hydrophilicporous membrane as a support membrane that supports the gel membranecontaining the CO₂ carrier and the CO₂ hydration catalyst.

Specifically, the present facilitated transport membrane includes, as amaterial of the separation-functional membrane, a copolymer including afirst structural unit derived from an acrylic acid cesium salt or anacrylic acid rubidium salt and a second structural unit derived fromvinyl alcohol (hereinafter simply abbreviated as “the presentcopolymer”), and also includes, as the CO₂ carrier, for example, atleast one of an alkali metal carbonate such as cesium carbonate (Cs₂CO₃)or rubidium carbonate (Rb₂CO₃), an alkali metal bicarbonate such ascesium bicarbonate (CsHCO₃) or rubidium bicarbonate (RbHCO₃), and analkali metal hydroxide such as cesium hydroxide (CsOH) or rubidiumhydroxide (RbOH), preferably an alkali metal carbonate or an alkalimetal bicarbonate, more preferably cesium carbonate. The CO₂ hydrationcatalyst preferably includes an oxo acid compound. In particular, theCO₂ hydration catalyst preferably includes an oxo acid compound of atleast one element selected from group 14 elements, group 15 elements,and group 16 elements. The CO₂ hydration catalyst may be, for example,at least one of a tellurous acid compound, a selenious acid compound, anarsenious acid compound, and an orthosilicic acid compound. Morespecifically, the CO₂ hydration catalyst may be potassium tellurite(K₂TeO₃, melting point: 465° C.), lithium tellurite (Li₂O₃Te, meltingpoint: about 750° C.), potassium selenite (K₂O₃Se, melting point: 875°C.), sodium arsenite (NaO₂As, melting point: 615° C.), sodiumorthosilicate (Na₄O₄Si, melting point: 1,018° C.), or the like. Atellurous acid compound is preferably used, and potassium tellurite ismore preferably used.

All the CO₂ hydration catalysts used in this embodiment are soluble inwater and extremely thermally stable with a melting point of 400° C. orhigher, and have catalytic activity at a high temperature of 100° C. orhigher. The melting point of the CO₂ hydration catalyst is only requiredto be higher than the upper limit of fluctuating temperatures in thesteps of a method for producing the present facilitated transportmembrane described later (e.g. the temperature in the medium removingstep or the thermal crosslinking temperature). When the melting pointis, for example, about 200° C. or higher, a situation can be avoided inwhich the CO₂ hydration catalyst is sublimed in the course of theproduction process so that the concentration of the CO₂ hydrationcatalyst in the separation-functional membrane decreases.

The first structural unit of the present copolymer is represented by thestructural formula below (Chemical Formula 5). In Chemical Formula 5, Mrepresents cesium or rubidium. The second structural unit of the presentcopolymer is represented by the structural formula below (ChemicalFormula 6). Hereinafter, it will be assumed that the present copolymeris a copolymer composed of a polymer of the first structural unit(poly(acrylic acid cesium salt) or poly(acrylic acid rubidium salt)) anda polymer of the second structural unit (polyvinyl alcohol) (a PVA/PAAcesium salt copolymer or a PVA/PAA rubidium salt copolymer).

The present copolymer may further include an additional structural unit(hereinafter referred to as “the third structural unit” as needed) otherthan the first and second structural units. The total content of thefirst and second structural units is preferably from 40 mol % to 100 mol%, more preferably from 50 mol % to 100 mol %, even more preferably from60 mol % to 100 mol %, with respect to the total content of all thestructural units constituting the present copolymer. In the presentcopolymer, a content of the second structural unit is preferably from 1mol % to 90 mol %, more preferably from 5 mol % to 85 mol %, even morepreferably from 10 mol % to 80 mol %, with respect to the total contentof the first and second structural units. In the present copolymer, thecontent of the second structural unit may be exemplified by, forexample, from 1 mol % to 90 mol %, from 5 mol % to 85 mol %, from 10 mol% to 80 mol %, from 20 mol % to 80 mol %, from 30 mol % to 80 mol %, orfrom 40 mol % to 80 mol %, with respect to the total content of thefirst and second structural units.

The third structural unit may be, for example, a structural unit derivedfrom a vinyl ester of a fatty acid of 2 to 16 carbon atoms, such asvinyl acetate, vinyl propionate, vinyl butyrate, vinyl laurate, vinylcaproate, vinyl stearate, vinyl palmitate, or vinyl versatate; astructural unit derived from an acrylic acid alkyl ester having an alkylgroup of 1 to 16 carbon atoms, such as methyl acrylate, ethyl acrylate,propyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, orlauryl acrylate; a structural unit derived from a methacrylic acid alkylester having an alkyl group of 1 to 16 carbon atoms, such as ethylmethacrylate, propyl methacrylate, butyl methacrylate, hexylmethacrylate, octyl methacrylate, or lauryl methacrylate; a structuralunit derived from a maleic acid dialkyl ester having an alkyl group of 1to 16 carbon atoms, such as dimethyl maleate, diethyl maleate, dibutylmaleate, dioctyl maleate, or dilauryl maleate; a structural unit derivedfrom a fumaric acid dialkyl ester having an alkyl group of 1 to 16carbon atoms, such as dimethyl fumarate, diethyl fumarate, dibutylfumarate, dioctyl fumarate, or dilauryl fumarate; a structural unitderived from an itaconic acid dialkyl ester having an alkyl group of 1to 16 carbon atoms, such as diethyl itaconate, dibutyl itaconate,dihexyl itaconate, dioctyl itaconate, or dilauryl itaconate; astructural unit derived from acrylic acid; or the like. The thirdstructural unit is preferably a structural unit derived from a vinylester of a fatty acid of 2 to 16 carbon atoms or a structural unitderived from an acrylic acid alkyl ester having an alkyl group of 1 to16 carbon atoms, more preferably a structural unit derived from a vinylester of a fatty acid of 2 to 4 carbon atoms or a structural unitderived from an acrylic acid alkyl ester having an alkyl group of 1 to 4carbon atoms, even more preferably a structural unit derived from vinylacetate or a structural unit derived from methyl acrylate.

The present resin composition includes the present copolymer, the CO₂carrier, and the CO₂ hydration catalyst. A content of the CO₂ carrier ispreferably form 20% by weight to 90% by weight, more preferably from 45%by weight to 85% by weight with respect to the total weight of the CO₂carrier and the present copolymer. The CO₂ hydration catalyst isgenerally added in a content of 0.01 to 1 mole, preferably 0.02 to 0.5moles, more preferably 0.025 to 0.5 moles per mole of the CO₂ carrier.

The present resin composition can be produced by a method including thestep of mixing the present copolymer, the CO₂ carrier, and the CO₂hydration catalyst. In this mixing step, water is preferably furtheradded as a medium. When water is added, the amount of water added ispreferably such that the resultant resin composition can be in the formof a uniform solution when used as a coating liquid as described later.The mixing order is not limited, and the mixing temperature ispreferably in the range of 5° C. to 90° C.

As an example, the present facilitated transport membrane is configuredas a three-layer structure in which a hydrophilic porous membrane 2supporting a separation-functional membrane 1 is held between twohydrophobic porous membranes 3 and 4 as schematically shown in FIG. 1.The separation-functional membrane 1 as a gel membrane is supported bythe hydrophilic porous membrane 2 and has a certain level of mechanicalstrength, and therefore is not necessarily required to be held betweenthe two hydrophobic porous membranes 3 and 4. The mechanical strengthcan also be increased by, for example, forming the hydrophilic porousmembrane 2 in a cylindrical shape. Therefore, the present facilitatedtransport membrane is not necessarily a flat plate-shaped one.

In the separation-functional membrane, a content of the presentcopolymer should be from about 10% by weight to about 80% by weight withrespect to the total weight of the present copolymer and the CO₂carrier, and a content of the CO₂ carrier should be from about 20% byweight to about 90% by weight with respect to the total weight of thepresent copolymer and the CO₂ carrier.

Further, the separation-functional membrane contains the CO₂ hydrationcatalyst, for example, in a content of not less than 0.01 times and notmore than 1 time, preferably not less than 0.02 times and not more than0.5 times, further preferably not less than 0.025 times and not morethan 0.5 times the content of the CO₂ carrier in terms of molar number.

The hydrophilic porous membrane preferably has heat resistance to atemperature of 100° C. or higher, mechanical strength and adhesion withthe separation-functional membrane (gel membrane) in addition tohydrophilicity, and preferably has a porosity (void ratio) of 55% ormore and a pore size falling within a range of 0.1 μm to 1 μm. In thisembodiment, a hydrophilized tetrafluoroethylene polymer (PTFE) porousmembrane is used as a hydrophilic porous membrane that satisfies theabove-mentioned requirements.

The hydrophobic porous membrane preferably has heat resistance to atemperature of 100° C. or higher, mechanical strength and adhesion withthe separation-functional membrane (gel membrane) in addition tohydrophobicity, and preferably has a porosity (void ratio) of 55% ormore and a pore size falling within a range of 0.1 μm to 1 μm. In thisembodiment, a non-hydrophilized tetrafluoroethylene polymer (PTFE)porous membrane is used as a hydrophobic porous membrane that satisfiesthe above-mentioned requirements.

One embodiment of a method for producing the present facilitatedtransport membrane (the present production method) will now be describedwith reference to FIG. 2. The following descriptions are based on theassumption that a PVA/PAA cesium salt copolymer is used as the presentcopolymer, cesium carbonate (Cs₂CO₃) is used as the CO₂ carrier, and atellurite (e.g. potassium tellurite (K₂TeO₃)) is used as the CO₂hydration catalyst. The contents of the hydrophilic polymer, the CO₂carrier and the CO₂ hydration catalyst are illustrative, and showcontents used in sample preparation in examples described below.

First, a coating liquid, corresponding to the present resin compositionincluding the present copolymer, the CO₂ carrier, and the CO₂ hydrationcatalyst, is prepared (step 1). More specifically, 2 g of a PVA/PAAcesium salt copolymer prepared by the present copolymer-producing methoddescribed below, 4.67 g of cesium carbonate, and a tellurite in a numberof moles 0.025 times the number of moles of cesium carbonate are addedto 80 g of water and mixed by stirring to form a coating liquid.

Next, the coating liquid obtained in step 1 is applied to a hydrophilicPTFE porous membrane side surface of a layered porous membrane by anapplicator (step 2). The layered porous membrane is obtained by joiningtwo membranes: a hydrophilic PTFE porous membrane (e.g. WPW-020-80manufactured by SUMITOMO ELECTRIC FINE POLYMER, INC.; thickness: 80 μm;pore size: 0.2 μm; void ratio: about 75%) and a hydrophobic PTFE porousmembrane (e.g. FLUOROPORE FP010 manufactured by SUMITOMO ELECTRIC FINEPOLYMER, INC.; thickness: 60 μm; pore size: 0.1 μm; void ratio: 55%).The thickness of the coating is 500 μm in the samples of Examples 1 to 7and Comparative Examples 1 and 2 described later, where the coatingliquid is applied once. In this process, the coating liquid penetratespores in the hydrophilic PTFE porous membrane, but is inhibited frompenetrating at the boundary surface of the hydrophobic PTFE porousmembrane, so that the coating liquid does not permeate to the oppositesurface of the layered porous membrane, and there is no coating liquidon the hydrophobic PTFE porous membrane side surface of the layeredporous membrane. This makes handling easy.

Next, the coated hydrophilic PTFE porous membrane is naturally dried atroom temperature so that a separation-functional layer in the form of agel is deposited on the hydrophilic PTFE porous membrane (step 3). Inthis case, the separation-functional layer in the form of a gel is asolid separation-functional membrane clearly distinguishable from aliquid membrane.

In the present production method, the coating liquid is applied to thehydrophilic PTFE porous membrane side surface of the layered porousmembrane in step 2, and therefore, in step 3, the separation-functionalmembrane is not only formed on the surface (coated surface) of thehydrophilic PTFE porous membrane but also formed so as to fill pores, sothat defects (minute defects such as pinholes) are less likely to occur,which leads to an increase in the success rate of theseparation-functional membrane production. In step 3, it is desirable tofurther thermally crosslink the naturally dried PTFE porous membrane ata temperature of 80° C. to 160° C., preferably about 120° C., for a timeperiod of 10 minutes to 4 hours, preferably about 2 hours. All of thesamples in examples and comparative examples described later arethermally crosslinked.

Next, a hydrophobic PTFE porous membrane identical to the hydrophobicPTFE porous membrane of the layered porous membrane used in step 2 issuperimposed on a gel layer side surface of the hydrophilic PTFE porousmembrane obtained in step 3 to obtain the present facilitated transportmembrane of three layer structure including a hydrophobic PTFE porousmembrane/a separation-functional membrane supported by a hydrophilicPTFE porous membrane/a hydrophobic PTFE porous membrane as schematicallyshown in FIG. 1 (step 4). FIG. 1 schematically and linearly shows astate in which the separation-functional membrane 1 fills pores of thehydrophilic PTFE porous membrane 2.

In the present production method, the blending ratio of the CO₂ carrierand the CO₂ hydration catalyst can be adjusted in step 1 of producing acoating liquid, and therefore, as compared to a case where afterformation of a gel membrane that does not contain at least one of theCO₂ carrier and the CO₂ hydration catalyst, at least one of the CO₂carrier and the CO₂ hydration catalyst is added into the gel membrane,adjustment of the blending ratio can be more accurately and easilyperformed, leading to enhancement of membrane performance.

Thus, the present facilitated transport membrane prepared by followingsteps 1 to 4 can exhibit extremely high selective permeability tohydrogen even at a high temperature of 100° C. or higher, for example aCO₂ permeance of about 3×10⁻⁵ mol/(m²·s·kPa) (=90 GPU) or more and aCO₂/H₂ selectivity of about 100 or more.

Next, a method for producing the present copolymer will be described.The present copolymer can be obtained by, for example, a productionmethod including the step of saponifying, with cesium hydroxide orrubidium hydroxide, a copolymer including a structural unit derived froman acrylic acid alkyl ester and a structural unit derived from a fattyacid vinyl ester (step A).

The present copolymer-producing method may further include the step ofpolymerizing at least an acrylic acid alkyl ester and a fatty acid vinylester to form the copolymer for use in step A (step a).

The acrylic acid alkyl ester may be an acrylic acid alkyl ester havingan alkyl group of 1 to 16 carbon atoms, and the fatty acid vinyl estermay be a vinyl ester of a fatty acid of 2 to 16 carbon atoms. They maybe polymerized according to, for example, the method described inJapanese Patent Application Publication NO. 52-107096 and JapanesePatent Application Publication NO. 52-27455.

In step A, the saponification is preferably performed in the presence ofwater and/or a water-soluble organic solvent (e.g., a C1 to C3 alcoholsolvent). The saponification temperature is preferably in the range of20° C. to 80° C., more preferably in the range of 25° C. to 75° C.

In step A, the structural unit derived from the acrylic acid alkyl esteris saponified to the first structural unit, and the structural unitderived from the fatty acid vinyl ester is saponified to the secondstructural unit. Therefore, when the degree of saponification iscontrolled or when neutralization is performed after the saponification,the present copolymer can contain, as the third structural unit, astructural unit derived from the fatty acid vinyl ester, a structuralunit derived from the acrylic acid alkyl ester, or a structural unitderived from acrylic acid.

It will be understood that in step a, the amount of a compound (otherthan the fatty acid vinyl ester and the acrylic acid alkyl ester) usedto derive the third structural unit, the degree of polymerization, orother factors may also be controlled so that the present copolymer cancontain the third structural unit.

As described above, conditions for step A or step a may be appropriatelyselected so that the content of the first and second structural unitscan be controlled in the above range.

Hereinafter, specific performance of the present facilitated transportmembrane is evaluated by comparing the performance of each of themembranes of Examples 1 to 7 and Comparative Examples 1 and 2. InExamples 1 to 7, the present copolymer (PVA/PAA cesium salt copolymer)is used as a hydrophilic polymer to form a separation-functionalmembrane, and a CO₂ hydration catalyst is contained in theseparation-functional membrane. In Comparative Examples 1 and 2, aPVA/PAA sodium salt copolymer, in which the alkali metal used to formthe acrylate differs from that in the present copolymer, is used as ahydrophilic polymer, and no CO₂ hydration catalyst is contained in theseparation-functional membrane.

A PVA/PAA cesium salt copolymer, corresponding to the present polymer,used in Examples 1 to 7 was produced according to the procedures shownin Synthesis Example 1 and Production Example 1 below.

(Synthesis Example 1) Synthesis of Vinyl Acetate-Methyl AcrylateCopolymer

A 2-L-volume reaction vessel equipped with a stirrer, a thermometer, aN₂ gas inlet tube, a reflux condenser, and dropping funnels was chargedwith 768 g of water and 12 g of anhydrous sodium sulfate, and the air inthe system was replaced by N₂ gas. The vessel was then charged with 1 gof partially saponified polyvinyl alcohol (88% in saponification degree)and 1 g of lauryl peroxide. After the internal temperature was raised to60° C., 104 g (1.209 mol) of methyl acrylate and 155 g (1.802 mol) ofvinyl acetate as monomers were each simultaneously added dropwise from adropping funnel for each monomer over 4 hours. During the dropwiseaddition, the internal temperature was kept at 60° C. at a stirring rateof 600 rpm. After the dropwise addition was completed, the mixture wasfurther stirred for 2 hours at an internal temperature of 65° C. Theresultant mixture was then dewatered by centrifugation, so that 288 g ofa vinyl acetate-methyl acrylate copolymer (with a water content of10.4%) was obtained.

(Production Example 1) Production of PVA/PAA Cesium Salt Copolymer

A 2-L-volume reaction vessel equipped with a stirrer, a thermometer, aN₂ gas inlet tube, a reflux condenser, and dropping funnels was chargedwith 500 g of methanol, 410 g of water, 554.2 g (3.3 mol) of cesiumhydroxide monohydrate, and 288 g of the vinyl acetate-methyl acrylatecopolymer (with a water content of 10.4%) obtained in SynthesisExample 1. The mixture was subjected to saponification under 400 rpmstirring at 30° C. for 3 hours. After the saponification was completed,the resultant reaction mixture was washed three times with 600 g ofmethanol, filtered, and dried at 70° C. for 6 hours to give 308 g of avinyl alcohol-cesium acrylate copolymer. Subsequently, 308 g of thevinyl alcohol-cesium acrylate copolymer was pulverized with a jet mill(LJ manufactured by Nippon Pneumatic Mfg. Co., Ltd.), so that 280 g offine powder of the vinyl alcohol-cesium acrylate copolymer was obtained.

The samples in Examples 1 to 7 and Comparative Examples 1 and 2 belowwere each prepared in accordance with the present production methoddescribed above. The weight of each of water, the hydrophilic polymer,and the CO₂ carrier in the coating liquid prepared in step 1 was asfollows. In Examples 1 to 3 and 7 and Comparative Examples 1 and 2, 80 gof water was mixed with 2 g of the hydrophilic polymer and 4.67 g of theCO₂ carrier. In Examples 4 to 6, 80 g of water was mixed with 3 g of thehydrophilic polymer and 7 g of the CO₂ carrier. In all Examples 1 to 7and Comparative Examples 1 and 2, the weight ratio of the hydrophilicpolymer to the CO₂ carrier is 3:7.

In Examples 1 to 7, the PVA/PAA cesium salt copolymer with no thirdstructural unit was used as the hydrophilic polymer. In ComparativeExamples 1 and 2, a PVA/PAA sodium salt copolymer without any structuralunit other than those derived from the acrylic acid salt and vinylalcohol was used as the hydrophilic polymer. In all Examples 1 to 7 andComparative Examples 1 and 2, the content of the acrylic acid salt inthe hydrophilic polymer is 40 mol % with respect to the total content ofthe copolymer. The CO₂ carrier used was cesium carbonate (Cs₂CO₃) exceptfor that used in Example 7 and Comparative Example 2. Rubidium carbonate(Rb₂CO₃) was used as the CO₂ carrier in Example 7 and ComparativeExample 2.

Potassium tellurite was used as the CO₂ hydration catalyst in Examples 1to 4 and 7, and sodium arsenite and potassium selenite were used as theCO₂ hydration catalyst in Examples 5 and 6, respectively. The molarratio of the CO₂ hydration catalyst to the CO₂ carrier is 0.025 times inExamples 1 and 4 to 6, 0.1 times in Example 2, 0.2 times in Example 3,and 0.05 times in Example 7.

The sample in Comparative Example 1 was prepared as in Example 1, exceptthat the coating liquid prepared in step 1 of the above productionmethod contained no CO₂ hydration catalyst and that the hydrophilicpolymer in the coating liquid was the sodium salt. The sample inComparative Example 2 was prepared as in Example 7, except that thecoating liquid prepared in step 1 of the above production methodcontained no CO₂ hydration catalyst and that the hydrophilic polymer inthe coating liquid was the sodium salt.

An experiment method for evaluating membrane performance of the samplesin Examples 1 to 7 and Comparative Examples 1 and 2 will now bedescribed.

Each sample was used while being fixed between a feed side chamber and apermeate side chamber in a stainless steel flow type gas permeation cellusing a fluororubber gasket as a seal material. Experimental conditionsare the same for the samples, and the temperature of the inside of thecell (hereinafter, referred to as “the treatment temperature”) is fixedat 130° C.

The feed side gas supplied to the feed side chamber is a mixed gasincluding CO₂, H₂ and H₂O (steam), and the ratio (mol %) among them isCO₂:H₂:H₂O=23.6:35.4:41.0. The flow rate of the feed side gas is3.47×10⁻² mol/min, and the feed side pressure is 600 kPa (A). (A) meansan absolute pressure. Accordingly, the CO₂ partial pressure on the feedside is 142 kPa (A). The pressure of the feed side chamber is adjustedwith a back pressure regulator provided on the downstream side of acooling trap at some midpoint in a retentate gas discharging passage.

On the other hand, the pressure of the permeate side chamber isatmospheric pressure, H₂O (steam) is used as a sweep gas made to flowinto the permeate side chamber, and the flow rate thereof is 7.77×10⁻³mol/min. For sending the sweep gas discharged from the permeate sidechamber to a gas chromatograph on the downstream side, an Ar gas isinpoured, steam in the gas containing the Ar gas is removed by thecooling trap, the composition of the gas after passing through thecooling trap is quantitatively determined by the gas chromatograph, thepermeance [mol/(m²·s·kPa)] of each of CO₂ and H₂ is calculated from thecomposition and the flow rate of Ar in the gas, and from the ratiothereof, the CO₂/H₂ selectivity is calculated.

In the evaluation experiment described above, the experiment apparatushas a pre-heater for heating the gas and the flow type gas permeationcell with a sample membrane fixed therein is placed in a thermostaticoven in order to keep constant the use temperature of the facilitatedtransport membrane of each sample and the temperatures of the feed sidegas and the sweep gas.

Next, a comparison is made of the membrane performance obtained as aresult of experiments in Examples 1 to 7 and Comparative Examples 1 and2. FIG. 3 shows a list of constitutional conditions (the CO₂ carrier,the CO₂ hydration catalyst, the molar ratio of the CO₂ carrier to theCO₂ hydration catalyst, the hydrophilic polymer, and the concentrationsof the hydrophilic polymer and the CO₂ carrier in the coating liquid)and membrane performance (CO₂ permeance, H₂ permeance, and CO₂/H₂selectivity) for the separation-functional membrane samples in Examples1 to 7 and Comparative Examples 1 and 2. Note that the concentrations(wt %) of the hydrophilic polymer and the CO₂ carrier shown in FIG. 3are approximate values calculated without taking into account the weightof the CO₂ hydration catalyst in the coating liquid.

First, the membrane performance is compared among Examples 1 to 3 and 7and Comparative Examples 1 and 2. The comparison of the membraneperformance is made with respect to the difference in hydrophilicpolymer, the presence or absence of the CO₂ hydration catalyst, and thedifference in the content of the CO₂ hydration catalyst. FIG. 4 shows,in the form of a graph, the CO₂ permeance and CO₂/H₂ selectivity inExamples 1 to 3 and 7 and Comparative Examples 1 and 2. FIGS. 3 and 4show the following. When the present copolymer is used as thehydrophilic polymer and the separation-functional membrane contains theCO₂ hydration catalyst in the case where the CO₂ carrier is cesiumcarbonate, the CO₂ permeance increases by a factor of 2.34 to 2.80 whilethe H₂ permeance increases by a factor of 1.14 to 1.52, and theincreasing rate of CO₂ permeance is greater than that of H₂ permeance,so that the CO₂/H₂ selectivity is significantly improved to be 128 to195 (1.62 to 2.46 times in terms of the increasing rate) as compared toa CO₂/H₂ selectivity of 79.2 in Comparative Example 1. Also in the casewhere the CO₂ carrier is rubidium carbonate, the CO₂ permeance increasesby a factor of 2.53 while the H₂ permeance increases by a factor of1.67, and the increasing rate of CO₂ permeance is greater than that ofH₂ permeance, so that the CO₂/H₂ selectivity is significantly improvedto be 141 (1.51 times in terms of the increasing rate) as compared to aCO₂/H₂ selectivity of 93.1 in Comparative Example 2.

A comparison among Examples 1 to 3 with reference to FIGS. 3 and 4 showsthat as the mixing ratio (molar ratio) of the CO₂ hydration catalyst tothe CO₂ carrier increases, the CO₂ permeance tends to increase, and evenwhen the molar ratio is 0.025, the increase in the CO₂ permeance and theimprovement of the CO₂/H₂ selectivity are apparent. A comparison betweenExamples 1 and 7 shows that the difference in the CO₂ carrier used doesnot make a significant difference in the increase in the CO₂ permeanceor the improvement of the CO₂/H₂ selectivity.

Next, the membrane performance is compared among Examples 4 to 6. Thecomparison of the membrane performance is made with respect to the typeof the CO₂ hydration catalyst. FIG. 5 shows, in the form of a graph, theCO₂ permeance and the CO₂/H₂ selectivity in Examples 4 to 6. FIGS. 3 and5 show that while all of the CO₂ hydration catalysts are found toimprove both the CO₂ permeance and the CO₂/H₂ selectivity, the CO₂permeance is remarkably improved using a tellurite.

Next, the membrane performance is compared among Examples 1 to 7.Specifically, a comparison of the membrane performance between Examples1 and 4 is made with respect to the difference in the concentrations ofthe hydrophilic polymer and the CO₂ carrier in the coating liquidproduced in step 1 described above. FIG. 6 shows, in the form of agraph, the CO₂ permeance and the H₂ permeance in Examples 1 to 7.Example 4 is the same as Example 1 in the hydrophilic polymer, the CO₂hydration catalyst, and the mixing ratio thereof, but differs fromExample 1 in that the total weight of the hydrophilic polymer and theCO₂ carrier in the coating liquid in Example 4 is 1.5 times that inExample 1. Note that the concentration (wt %) of the hydrophilic polymerand the CO₂ carrier in the coating liquid in Example 4 is about 1.44times that in Example 1.

First, a comparison between Examples 1 and 4 with reference to FIGS. 3and 6 shows that the CO₂ permeance in Example 1 (6.61×10⁻⁵mol/(m²·s·kPa)) and the CO₂ permeance in Example 4 (6.93×10⁻⁵mol/(m²·s·kPa)) are almost the same, with a difference of only few %,but the H₂ permeance in Example 4 (3.28×10⁻⁷ mol/(m²·s·kPa)) is smallerthan the H₂ permeance in Example 1 (5.18×10⁻⁷ mol/(m²·s·kPa)).Therefore, Example 4 is superior in CO₂/H₂ selectivity to Example 1.

The CO₂ permeation mechanism is a facilitated transport mechanism.Therefore, no significant difference in CO₂ permeance occurs betweenExamples 1 and 4 because they are the same in the hydrophilic polymer,the type and concentration of the CO₂ carrier in the gel membrane, andthe type and mixing ratio of the CO₂ hydration catalyst, namely, theyare the same in major factors capable of influencing the CO₂ permeance.On the other hand, since H₂ does not react with the CO₂ carrier, the H₂permeation mechanism is not a facilitated transport mechanism but asolution-diffusion mechanism. A comparison of the H₂ permeance betweenExamples 1 and 4 suggests that the difference may be influenced byindividual differences (fluctuations in production) in the quality ofthe hydrophilic polymer gel membrane.

In this case, the concentration of the hydrophilic polymer in thecoating liquid in Example 4 is 1.5 times that in Example 1. Therefore,the thickness of the gel membrane in Example 4 should be larger thanthat in Example 1, depending on the difference in the concentration, andtaking into account the H₂ permeation mechanism, the difference in H₂permeance between Examples 1 and 4 may be influenced by the differencein the thickness of the gel membrane. However, the H₂ permeance inExamples 5 and 6, where the concentration of the hydrophilic polymer inthe coating liquid is the same as that in Example 4, is greater thanthat in Example 3, where the concentration of the hydrophilic polymer inthe coating liquid is the same as that in Example 1. Therefore, thevariations in H₂ permeance should mainly result from individualdifferences in the quality of the gel membrane. The average H₂ permeancein Examples 4 to 6, where the concentration of the hydrophilic polymerin the coating liquid is 1.5 times that in Examples 1 to 3 and 7, is4.28×10⁻⁷ mol/(m²·s·kPa), whereas the average H₂ permeance in Examples 1to 3 and 7 is 4.94×10⁻⁷ mol/(m²·s·kPa), which is about 16% greater thanthat in Examples 4 to 6. Therefore, there is room to suppress theincrease in H₂ permeance by controlling the concentration of thehydrophilic polymer in the coating liquid.

According to the present facilitated transport membrane, theseparation-functional membrane includes the CO₂ hydration catalyst andthe present copolymer as a hydrophilic polymer. As shown above, thesefeatures allow a two-stage increase in CO₂ permeance and thus make itpossible to obtain a CO₂/H₂ selectivity of 100 or more. In addition,when the increase or variations in H₂ permeance is suppressed bycontrolling the weight content of the present copolymer in the coatingliquid, a CO₂/H₂ selectivity equal to or higher than that in Example 4can be achieved.

In Examples 1 to 7 and Comparative Examples 1 and 2 shown above, thecoating liquid was applied once to the surface of the porous membrane instep 2 of the method for producing the present facilitated transportmembrane, and the coating thickness was 500 μm. Examples 8 and 9 andComparative Example 3 were also performed, in which the application wasperformed twice to increase the coating thickness, and the membraneperformance was evaluated by the procedure described below.

The constitutional conditions and the production method for theseparation-functional membrane in Examples 8 and 9 are the same as thosein Example 1 except for the number of times of the application of thecoating liquid. The constitutional conditions and the production methodfor the separation-functional membrane in Comparative Example 3 are thesame as those in Comparative Example 1 except for the number of times ofthe application of the coating liquid.

The membrane performance in Example 8 was evaluated under anexperimental condition (condition B) different from that (condition A)in Examples 1 to 7, and the membrane performance in Example 9 andComparative Example 3 was evaluated under another experimental condition(condition C) different from that in Examples 1 to 7. The evaluationexperiments under conditions B and C were performed using a mixed gas ofCO₂, N₂, and H₂O (steam) as the feed side gas, in which nitrogen is usedinstead of hydrogen. Under conditions B and C, therefore, CO₂ and N₂permeance [mol/(m²·s·kPa)] and CO₂/N₂ selectivity are evaluated for themembrane performance. In this case, the feed side pressure underconditions B and C is 600 kPa (A), which is the same as that undercondition A, and the content (mol %) of CO₂ in the mixed gas underconditions B and C is set at 23.6%, which is also the same as that undercondition A. Therefore, the CO₂ partial pressure on the feed side underconditions B and C is 142 kPa (A), which is also the same as that undercondition A.

The experimental conditions for condition B are the same as those forcondition A, except that nitrogen is used as one component of the feedside gas instead of hydrogen. The treatment temperature 130° C. undercondition B differs from the treatment temperature 110° C. undercondition C.

FIG. 7 shows a list of constitutional conditions (the CO₂ carrier, theCO₂ hydration catalyst, the molar ratio of the CO₂ carrier to the CO₂hydration catalyst, the hydrophilic polymer conditions, theconcentrations of the hydrophilic polymer and the CO₂ carrier in thecoating liquid, and the number of times of the application), thetreatment temperature, and the membrane performance (CO₂ permeance, N₂permeance, and CO₂/N₂ selectivity) for the separation-functionalmembrane sample in each of Examples 8 and 9 and Comparative Example 3.

Referring to FIG. 7, a comparison of the evaluation results in Examples8 and 9 shows that as the treatment temperature decreases, both the CO₂permeance and the N₂ permeance decreases, but the CO₂/N₂ selectivityincreases because the N₂ permeance decreases more.

The samples in Example 9 and Comparative Example 3, where the membraneperformance is evaluated under condition C, differ in the constitutionalconditions and production method for the separation-functional membrane.Specifically, the sample in Comparative Example 3 is prepared as inExample 9, except that the coating liquid prepared in step 1 of theproduction method contains no CO₂ hydration catalyst and that thehydrophilic polymer in the coating liquid is a sodium salt. Thesedifferences are the same as those between the samples in Example 1 andComparative Example 2. Referring to FIG. 7, a comparison of theevaluation results in Example 9 and Comparative Example 3 shows that theCO₂ permeance is higher in Example 9, where the hydrophilic polymer is acesium salt and the CO₂ hydration catalyst is present, than inComparative Example 3, and there is no significant difference in N₂permeance between them, so that the CO₂/N₂ selectivity is improved inExample 9.

While all of the separation-functional membranes in Examples 1 to 9 andComparative Examples 1 to 3 are gel membranes, Comparative Example 4having a liquid membrane (aqueous solution) as a separation-functionalmembrane was prepared as another comparative example. The aqueoussolution of a separation-functional membrane in Comparative Example 4does not contain the PVA/PAA salt copolymer used in Examples 1 to 9 andComparative Examples 1 to 3. In Comparative Example 4, cesium carbonatewas used as a CO₂ carrier and potassium tellurite was used as a CO₂hydration catalyst similarly to Example 1. Hereinafter, a method forpreparing Comparative Example 4 will be described.

To an aqueous cesium carbonate solution having a molar concentration of2 mol/L was added potassium tellurite in a content of 0.025 times thecontent of cesium carbonate in terms of molar number, and the resultantmixture was stirred until potassium tellurite was dissolved, therebyobtaining an aqueous solution for a separation-functional membrane(liquid membrane). Thereafter, instead of the application method usingan applicator in step 2 in the present production method, a hydrophilicPTFE porous membrane was immersed in the aqueous solution for aseparation-functional membrane (liquid membrane) for 30 minutes, and thehydrophilic PTFE membrane soaked with the aqueous solution was thenplaced on a hydrophobic PTFE membrane, and dried at room temperature forhalf a day or longer. Similarly to Examples 1 to 9 and ComparativeExamples 1 to 3, another hydrophobic PTFE membrane is placed on thehydrophilic PTFE membrane to form a three-layer structure with thehydrophilic PTFE porous membrane and the separation-functional membrane(liquid membrane) held between the hydrophobic PTFE membranes at thetime of an experiment for evaluation of membrane performance.

However, in the case of the liquid membrane sample of ComparativeExample 4, it was impossible to set the feed side pressure of 600 kPa(A), i.e. an experimental condition similar to that in Examples 1 to 9and Comparative Examples 1 to 3, and membrane performance could not beevaluated. That is, it became evident that a necessary differentialpressure cannot be maintained because the difference in pressure betweenthe feed side and the permeate side in the separation-functionalmembrane (liquid membrane) cannot be endured.

In Examples 1 to 7, CO₂ permeance, H₂ permeance, CO₂/H₂ selectivity areevaluated for the specific performance of the present facilitatedtransport membrane, and improvements in CO₂ permeance and selectivepermeability of CO₂ to hydrogen are successfully demonstrated. Also whena mixed gas containing nitrogen, methane, or other non-hydrogen gas witha molecular weight higher than that of hydrogen is used as the feed sidegas and supplied to the feed side chamber, higher CO₂ selectivepermeability can be, of course, achieved as is apparent from theevaluation results in Example 9 and Comparative Example 3, because themechanism for the permeation of nitrogen or other gas with a highermolecular weight is not a facilitated transport mechanism but asolution-diffusion mechanism.

Second Embodiment

Next, a description will be given of a CO₂ separation membrane module, aCO₂ separation apparatus, and a CO₂ separation method, which aredesigned to use the facilitated CO₂ transport membrane shown in thefirst embodiment.

The present facilitated transport membrane is preferably used to form aCO₂ separation membrane module. A CO₂ separation apparatus according tothis embodiment includes the facilitated CO₂ transport membrane or theCO₂ separation membrane module, a gas supply unit configured to supply aCO₂-containing mixed gas to the facilitated CO₂ transport membrane, anda gas separation unit configured to separate from the mixed gas CO₂having permeated the facilitated CO₂ transport membrane.

Examples of the type of the CO₂ separation membrane module include aspiral type, a cylindrical type, a hollow fiber type, a pleated type, aplate-and-frame type, and the like. The facilitated CO₂ transportmembrane of the present invention may also be used in a process combinedwith a decarbonation technique such as chemical absorption, adsorption,or cryogenic separation. Examples include an apparatus for separatingand collecting CO₂ by using a combination of membrane separation andchemical absorption as described in U.S. Pat. No. 4,466,946; and anapparatus for separating and collecting gas by a membrane-absorptionhybrid method, in which an absorbing liquid is used in combination witha membrane, as described in Japanese Patent Application Publication NO.2007-297605.

Hereinafter, a CO₂ separation apparatus including a cylindrical CO₂separation membrane module will be described with reference to FIGS. 8Aand 8B.

FIGS. 8A and 8B are each a sectional view schematically showing theoutlined structure of a CO₂ separation apparatus 10 of this embodiment.In this embodiment, as an example, a facilitated CO₂ transport membranemodified to have a cylindrical structure is used to form a CO₂separation membrane module, instead of the facilitated CO₂ transportmembrane of a flat plate structure shown in the first embodiment. FIG.8A shows a cross-sectional structure at a cross section perpendicular tothe axial center of a facilitated CO₂ transport membrane (the presentfacilitated transport membrane) 11 of a cylindrical structure, and FIG.8B shows a cross-sectional structure at a cross section extendingthrough the axial center of the present facilitated transport membrane11.

The present facilitated transport membrane 11 shown in FIGS. 8A and 8Bhas a structure in which a separation-functional membrane 1 is supportedon the outer circumferential surface of a cylindrical hydrophilicceramic porous membrane 2. Similarly to the first embodiment, theseparation-functional membrane 1 includes the present copolymer as amembrane material; a CO₂ carrier composed of, for example, at least oneof an alkali metal carbonate such as cesium carbonate (Cs₂CO₃) orrubidium carbonate (Rb₂CO₃), an alkali metal bicarbonate such as cesiumbicarbonate (CsHCO₃) or rubidium bicarbonate (RbHCO₃), and an alkalimetal hydroxide such as cesium hydroxide (CsOH) or rubidium hydroxide(RbOH); and a CO₂ hydration catalyst composed of, for example, at leastone of a tellurous acid compound, a selenious acid compound, anarsenious acid compound, and an orthosilicic acid compound. The membranestructure in this embodiment is different from the membrane structure inthe first embodiment in that the separation-functional membrane 1 andthe hydrophilic ceramic porous membrane 2 are not held between twohydrophobic porous membranes. The method for producing theseparation-functional membrane 1 and the membrane performance thereof inthis embodiment are basically similar to those in the first embodimentexcept for the above difference, and therefore duplicate explanationswill be omitted.

As shown in FIGS. 8A and 8B, the present cylindrical facilitatedtransport membrane 11 is housed in a bottomed cylindrical container 12,and a feed side space 13 surrounded by the inner wall of the container12 and the separation-functional membrane 1 and a permeate side space 14surrounded by the inner wall of the ceramic porous membrane 2 areformed. A first feeding port 15 for feeding a source gas FG into thefeed side space 13 and a second feeding port 16 for feeding a sweep gasSG into the permeate side space 14 are provided on one of bottomportions 12 a and 12 b on opposite sides of the container 12, and afirst discharge port 17 for discharging a CO₂-separated source gas EGfrom the feed side space 13 and a second discharge port 18 fordischarging from the permeate side space 14 a discharge gas SG′including a mixture of a CO₂-containing permeate gas PG having permeatedthe present facilitated transport membrane 11 and the sweep gas SG areprovided on the other of the bottom portions 12 a and 12 b on oppositesides of the container 12. The container 12 is made of, for example,stainless steel, and although not illustrated, the present facilitatedtransport membrane 11 is fixed in the container 12 with a fluororubbergasket interposed as a seal material between opposite ends of thepresent facilitated transport membrane 11 and the inner walls of thebottom portions 12 a and 12 b on opposite sides of the container 12similarly to the experiment apparatus described in the first embodimentas an example. The method for fixing the present facilitated transportmembrane 11 and the sealing method are not limited to the methodsdescribed above.

In FIG. 8B, each of the first feeding port 15 and the first dischargeport 17 is provided in each of the feed side spaces 13 illustratedseparately on the left and the right in FIG. 8B. However, since the feedside spaces 13 annularly communicate with each other as shown in FIG.8A, the first feeding port 15 and the first discharge port 17 may beprovided in one of the left and right feed side spaces 13. Further, FIG.8B shows as an example a configuration in which the first feeding port15 and the second feeding port 16 are provided on one of the bottomportions 12 a and 12 b, and the first discharge port 17 and the seconddischarge port 18 are provided on the other of the bottom portions 12 aand 12 b, but a configuration may be employed in which the first feedingport 15 and the second discharge port 18 are provided on one of thebottom portions 12 a and 12 b, and the first discharge port 17 and thesecond feeding port 16 are provided on the other of the bottom portions12 a and 12 b. That is, the direction along which the source gases FGand EG flow and the direction along which the sweep gas SG and thedischarge gas SG′ flow may be reversed.

In the CO₂ separation method of this embodiment, the source gas FGincluding a CO₂-containing mixed gas is fed into the feed side space 13and thereby supplied to the feed side surface of the present facilitatedtransport membrane 11, so that the CO₂ carrier in theseparation-functional membrane 1 of the present facilitated transportmembrane 11 is reacted with CO₂ in the source gas FG to allow selectivepassage of CO₂ at a high selective permeation rate, and the source gasEG with a reduced CO₂ concentration, resulting from the CO₂ separation,is discharged from the feed side space 13.

The reaction of CO₂ with the CO₂ carrier requires supply of water (H₂O)as shown in the above reaction formula of (Chemical Formula 2), and asthe amount of water contained in the separation-functional membrane 1increases, chemical equilibrium is shifted to the product side (rightside), so that permeation of CO₂ is facilitated. When the temperature ofthe source gas FG is a high temperature of 100° C. or higher, theseparation-functional membrane 1 that is in contact with the source gasFG is also exposed to a high temperature of 100° C. or higher, so thatwater contained in the separation-functional membrane 1 is evaporatedand passes into the permeate side space 14 similarly to CO₂, andtherefore it is necessary to supply steam (H₂O) to the feed side space13. The steam may be contained in the source gas FG, or may be suppliedto the feed side space 13 independently of the source gas FG. In thelatter case, steam (H₂O) passing into the permeate side space 14 may beseparated from the discharge gas SG′ and circulated into the feed sidespace 13.

For the CO₂ separation apparatus shown in FIGS. 8A and 8B, aconfiguration example has been described in which the feed side space 13is formed at the outside while the permeate side space 14 is formed atthe inside of the present cylindrical facilitated transport membrane 11,but the feed side space 13 may be formed at the inside while thepermeate side space 14 may be formed at the outside. The presentfacilitated transport membrane 11 may have a structure in which theseparation-functional membrane 1 is supported on the innercircumferential surface of the cylindrical hydrophilic ceramic porousmembrane 2. Further, the present facilitated transport membrane 11 usedin the CO₂ separation apparatus is not necessarily cylindrical, but maybe in the form of a tube having a cross-sectional shape other than acircular shape, and the present facilitated transport membrane of flatplate structure as shown in FIG. 1 may be used.

As an application example of the CO₂ separation apparatus, a shiftconverter (CO₂ permeable membrane reactor) including the presentfacilitated transport membrane will now be briefly described.

For example, when a CO₂ permeable membrane reactor is formed using theCO₂ separation apparatus 10 shown in FIGS. 8A and 8B, the feed sidespace 13 can be used as a shift converter by filling the feed side space13 with a shift catalyst.

The CO₂ permeable membrane reactor is an apparatus in which, forexample, a source gas FG produced in a steam reforming device and havingH₂ as a main component is received in the feed side space 13 filled witha shift catalyst, and carbon monoxide (CO) contained in the source gasFG is removed through a CO shift reaction expressed by the following(Chemical Formula 7). CO₂ produced through the CO shift reaction isallowed to permeate to the permeate side space 14 selectively by meansof the present facilitated transport membrane 11 and removed, wherebychemical equilibrium can be shifted to the hydrogen production side, sothat CO and CO₂ can be removed beyond the limit imposed by equilibriumrestriction with a high conversion rate at the same reactiontemperature. A source gas EG freed of CO and CO₂ and having H₂ as a maincomponent is taken out from the feed side space 13.CO+H₂O

CO₂+H₂  (Chemical Formula 7)

Since the performance of the shift catalyst used for the CO shiftreaction tends to decrease with a decrease in temperature, the usetemperature is considered to be 100° C. at minimum, and the temperatureof the source gas FG supplied to the feed side surface of the presentfacilitated transport membrane 11 is 100° C. or higher. Therefore, thesource gas FG is adjusted to a temperature suitable for catalyticactivity of the shift catalyst, then fed into the feed side space 13filled with the shift catalyst, subjected to the CO shift reaction(exothermic reaction) in the feed side space 13, and supplied to thepresent facilitated transport membrane 11.

On the other hand, the sweep gas SG is used for maintaining the drivingforce for the permeation through the present facilitated transportmembrane 11 by lowering the partial pressure of the CO₂-containingpermeate gas PG which permeates the present facilitated transportmembrane 11 and for discharging the permeate gas PG to the outside. Itis to be noted that when the partial pressure of the source gas FG issufficiently high, it is not necessary to feed the sweep gas SG becausea partial pressure difference serving as the driving force forpermeation is obtained even if the sweep gas SG is not fed. As a gasspecies used for the sweep gas, steam (H₂O) can also be used as in thecase of the experiment for evaluation of membrane performance in thefirst embodiment, and further an inert gas such as Ar can also be used.The sweep gas SG is not limited to a specific gas species.

Other Embodiments

Hereinafter, other embodiments will be described.

<1> The above-mentioned embodiments have been described based on theassumption that a carbonate, a bicarbonate or a hydroxide of an alkalimetal such as cesium or rubidium is used as a CO₂ carrier. However,since the present invention is characterized in that a gel membraneincluding the present copolymer that forms a separation-functionalmembrane contains a CO₂ carrier and a CO₂ hydration catalyst havingcatalytic activity at a high temperature of 100° C. or higher, the CO₂carrier is not limited to a specific CO₂ carrier as long as it is such aCO₂ carrier that a reaction of CO₂ with the CO₂ carrier can beaccelerated by a CO₂ hydration catalyst to attain membrane performancecomparable to or higher than the membrane performance (selectivepermeability of CO₂ to hydrogen) shown as an example in the firstembodiment.

<2> The above-mentioned embodiments have been described based on theassumption that the CO₂ hydration catalyst contains at least one of atellurous acid compound, a selenious acid compound, an arsenious acidcompound and an orthosilicic acid compound, but the CO₂ hydrationcatalyst is not limited to a specific CO₂ hydration catalyst as long asit is a CO₂ hydration catalyst which has catalytic activity for the CO₂hydration reaction of the above (Chemical Formula 1) at a hightemperature of 100° C. or higher, preferably 130° C. or higher, morepreferably 160° C. or higher and which can attain membrane performancecomparable to or higher than the membrane performance (selectivepermeability of CO₂ to hydrogen) shown as an example in the firstembodiment when combined with a CO₂ carrier. When used in theseparation-functional membrane of the present facilitated transportmembrane, the CO₂ hydration catalyst is preferably one that has amelting point of 200° C. or higher and is soluble in water similarly tothe above-mentioned compounds. While the upper limit of the range oftemperatures at which the CO₂ hydration catalyst exhibits catalyticactivity is not particularly limited, there is no problem as long as itis higher than the upper limit of the range of temperatures such as theuse temperature of the present facilitated transport membrane in anapparatus including the present facilitated transport membrane, and thetemperature of a source gas supplied to the feed side surface of thepresent facilitated transport membrane. The hydrophilic porous membraneor the like that forms the present facilitated transport membrane isalso required to have resistance in a similar temperature range as amatter of course. When the present facilitated transport membrane isused at a temperature lower than 100° C., the CO₂ hydration catalyst isnot necessarily required to have catalytic activity at a hightemperature of 100° C. or higher. In this case, the lower limit of thetemperature range where the CO₂ hydration catalyst exhibits catalyticactivity is preferably lower than 100° C. depending on the operatingtemperature range of the present facilitated transport membrane.

<3> In the first embodiment, the present facilitated transport membraneis prepared by applying, to the hydrophilic PTFE porous membrane, thecoating liquid containing the present copolymer, the CO₂ carrier, andthe CO₂ hydration catalyst. Alternatively, the present facilitatedtransport membrane may be prepared by a method other than the abovemethod. For example, the present facilitated transport membrane may beprepared by a process that includes forming a gel membrane including thepresent copolymer and being free of the CO₂ carrier and the CO₂hydration catalyst and then impregnating the gel membrane with anaqueous solution containing the CO₂ carrier and the CO₂ hydrationcatalyst. In addition, the porous membrane to which the coating liquidis to be applied is also not limited to a hydrophilic porous membrane.

<4> In the first embodiment, the present facilitated transport membranehas a three-layer structure including a hydrophobic PTFE porousmembrane, a separation-functional membrane supported by a hydrophilicPTFE porous membrane and a hydrophobic PTFE porous membrane, but thesupport structure of the present facilitated transport membrane is notlimited to such a three-layer structure. For example, the presentfacilitated transport membrane may have a two-layer structure includinga hydrophobic PTFE porous membrane and a separation-functional membranesupported by a hydrophilic PTFE porous membrane. The present facilitatedtransport membrane may also have a single-layer structure including aseparation-functional membrane supported by a hydrophilic PTFE porousmembrane. In the first embodiment, a case has been described where theseparation-functional membrane is supported by the hydrophilic PTFEporous membrane, but the separation-functional membrane may be supportedby the hydrophobic PTFE porous membrane.

<5> In the second embodiment, a CO₂ permeable membrane reactor has beenshown as an application example of the CO₂ separation apparatusincluding the present facilitated transport membrane. The CO₂ separationapparatus including the present facilitated transport membrane can alsobe used in a decarbonation process performed in a large-scale plant forhydrogen production, urea production, or the like, other than membranereactors. The CO₂ separation apparatus including the present facilitatedtransport membrane can also be used in applications other than hydrogenproduction process, such as separation of CO₂ from waste gases fromthermal power plants, ironworks, or the like and separation of CO₂during natural gas purification. The CO₂ separation apparatus is notlimited to the application example shown in the above embodiment. Thefeed side gas (source gas) supplied to the present facilitated transportmembrane is also not limited to the mixed gas shown as an example in theabove embodiments.

<6> The mixing ratios of the components in the composition of thepresent facilitated transport membrane, the dimensions of the portionsof the membrane and the like as shown as examples in the above-mentionedembodiments are examples given for easy understanding of the presentinvention, and the present invention is not limited to facilitated CO₂transport membranes having such values.

INDUSTRIAL APPLICABILITY

The facilitated CO₂ transport membrane according to the presentinvention can be used for separating CO₂ with a high selectivepermeability from a CO₂-containing mixed gas in the decarbonation stepof a large-scale process for hydrogen production, urea production, orthe like, and can also be used in CO₂ permeable membrane reactors andthe like.

DESCRIPTION OF SYMBOLS

-   -   1 separation-functional membrane    -   2 hydrophilic porous membrane    -   3, 4 hydrophobic porous membrane    -   10 CO₂ separation apparatus    -   11 facilitated CO₂ transport membrane    -   12 container    -   12 a, 12 b bottom portion (upper bottom portion and lower bottom        portion) of container    -   13 feed side space    -   14 permeate side space    -   15 first feeding port    -   16 second feeding port    -   17 first discharge port    -   18 second discharge port    -   FG source gas    -   EG CO₂-separated source gas    -   PG permeate gas    -   SG, SG′ sweep gas

The invention claimed is:
 1. A facilitated CO₂ transport membercomprising: a separation-functional membrane, the membrane being a gelmembrane of a hydrophilic polymer, the hydrophilic polymer comprising aCO₂ carrier and a CO₂ hydration catalyst, wherein the hydrophilicpolymer is a copolymer comprising a first structural unit represented byChemical Formula (1) shown below, where M represents cesium or rubidium,and a second structural unit represented by Chemical Formula (2) shownbelow, wherein the copolymer comprises a third structural unit selectedfrom a group consisting of a structural unit derived from a methacrylicacid alkyl ester having an alkyl group of 1 to 16 carbon atoms, astructural unit derived from a maleic acid dialkyl ester having an alkylgroup of 1 to 16 carbon atoms, a structural unit derived from a fumaricacid dialkyl ester having an alkyl group of 1 to 16 carbon atoms, and astructural unit derived from an itaconic acid dialkyl ester having analkyl group of 1 to 16 carbon atoms, and wherein the CO₂ hydrationcatalyst has catalytic activity at a temperature of 100° C. or higherand a melting point of 200° C. or higher


2. The facilitated CO₂ transport member according to claim 1, whereinthe CO₂ hydration catalyst is soluble in water.
 3. The facilitated CO₂transport member according to claim 1, wherein the CO₂ hydrationcatalyst comprises at least one of a tellurous acid compound, aselenious acid compound, an arsenious acid compound, and an orthosilicicacid compound.
 4. The facilitated CO₂ transport member according toclaim 1, wherein a content of the second structural unit in thehydrophilic polymer is from 1 mol % to 90 mol % with respect to thetotal content of the first and second structural units.
 5. Thefacilitated CO₂ transport member according to claim 1, wherein the CO₂carrier comprises at least one of an alkali metal carbonate, an alkalimetal bicarbonate, and an alkali metal hydroxide.
 6. The facilitated CO₂transport member according to claim 5, wherein an alkali metal includedin one of the alkali metal carbonate, the alkali metal bicarbonate, andthe alkali metal hydroxide is cesium or rubidium.
 7. The facilitated CO₂transport member according to claim 1, further comprising a hydrophilicporous membrane, wherein the separation-functional membrane is supportedby the hydrophilic porous membrane.
 8. A method for producing thefacilitated CO₂ transport member according to claim 1, the methodcomprising the steps of: coating a porous membrane with a coating liquidin which the hydrophilic polymer, the CO₂ carrier, the CO₂ hydrationcatalyst, and a medium containing water are included; and removing themedium from a resultant coating to produce the separation-functionalmembrane in the form of a gel.
 9. A CO₂ separating method comprising thesteps of: supplying a CO₂-containing mixed gas to the facilitated CO₂transport member according to claim 1; and separating from the mixed gasthe CO₂ having permeated the facilitated CO₂ transport member.
 10. A CO₂separation membrane module comprising the facilitated CO₂ transportmember according to claim
 1. 11. A CO₂ separation apparatus comprising:the facilitated CO₂ transport member according to claim 1; a firstfeeding port, a second feeding port, a first discharge port, and asecond discharge port, wherein: the first feeding port is configured tofeed a gas from a source of gas, including a CO₂-containing mixed gas,into a supply side of the facilitated CO₂ transport member; the secondfeeding port is configured to feed a sweep gas into a permeate side ofthe facilitated CO₂ transport member; the first discharge port isconfigured to discharge a CO₂-separated source gas from the supply sideof the facilitated CO₂ transport member; and the second discharge portis configured to discharge a CO₂-containing permeate gas from thepermeate side of the facilitated CO₂ transport member.
 12. A resincomposition comprising: a CO₂ carrier; a CO₂ hydration catalyst; and acopolymer comprising a first structural unit represented by ChemicalFormula (1) shown below, where M represents cesium or rubidium, and asecond structural unit represented by Chemical Formula (2) shown below,wherein the copolymer comprises a third structural unit selected from agroup consisting of a structural unit derived from a methacrylic acidalkyl ester having an alkyl group of 1 to 16 carbon atoms, a structuralunit derived from a maleic acid dialkyl ester having an alkyl group of 1to 16 carbon atoms, a structural unit derived from a fumaric aciddialkyl ester having an alkyl group of 1 to 16 carbon atoms, and astructural unit derived from an itaconic acid dialkyl ester having analkyl group of 1 to 16 carbon atoms, and wherein the CO₂ hydrationcatalyst has catalytic activity at a temperature of 100° C. or higherand a melting point of 200° C. or higher


13. The resin composition according to claim 12, wherein the CO₂hydration catalyst is soluble in water.
 14. The resin compositionaccording to claim 12, wherein the CO₂ hydration catalyst comprises anoxo acid compound.
 15. The resin composition according to claim 12,wherein the CO₂ hydration catalyst comprises at least one of a tellurousacid compound, a selenious acid compound, an arsenious acid compound,and an orthosilicic acid compound.
 16. The resin composition accordingto claim 12, wherein a content of the second structural unit is from 1mol % to 90 mol % with respect to the total content of the first andsecond structural units.
 17. The resin composition according to claim12, wherein the CO₂ carrier comprises at least one of an alkali metalcarbonate, an alkali metal bicarbonate, and an alkali metal hydroxide.18. The resin composition according to claim 17, wherein an alkali metalincluded in one of the alkali metal carbonate, the alkali metalbicarbonate, and the alkali metal is cesium or rubidium.
 19. The resincomposition according to claim 12, wherein a content of the CO₂ carrieris from 20% by weight to 90% by weight with respect to the total weightof the CO₂ carrier and the copolymer.
 20. The resin compositionaccording to claim 12, wherein the number of moles of the CO₂ hydrationcatalyst is at least 0.02 times the number of moles of the CO₂ carrier.